Changes In Myocardial Performance Research Articles

Normative Echocardiographic Values for Right and Left Ventricular Function in Extremely Premature Neonates

To identify the measures of biventricular function and surrogates of pulmonary vascular resistance that can be expected in relatively stable extremely premature neonates, and evaluate maturational changes in myocardial performance in this patient population. This was a prospective observational study. Clinically stable extremely preterm newborns were divided into 3 cohorts based on gestational age: cohort 1 (240/7-256/7weeks), cohort 2 (260/7-276/7weeks), and cohort 3 (280/7-296/7weeks). Serial echocardiograms were obtained on day of life 3-5, 7-10, and just prior to discharge. In total, 46 subjects met the criteria aimed at capturing only the most clinically healthy and stable newborns less than 296/7weeks of gestational age. Myocardial performance was reliably assessed by echocardiography with high inter-reader correlation. Normative values were identified for right ventricular function, left ventricular function, and surrogates of pulmonary vascular resistance. Biventricular systolic performance is significantly different in the clinically stable extremely premature neonate when compared with healthy full-term newborns. All participants had evidence of poor biventricular compliance at birth which improved with maturation. Extreme prematurity does not appear to adversely affect myocardial functional maturation at the time of term corrected age and/or discharge.

Tissue Doppler echocardiography detects subclinical left ventricular dysfunction in patients undergoing chemotherapy for colon cancer: insights from ONCOECHO multicentre study.

Colorectal cancer (CRC) is the second most common cancer in women and the third in men in Poland. The role of chemotherapy (CTX) depends on the stage of CRC: adjuvant CTX is a standard treatment in stage III and should also be considered in stage II with risk factors. The aim of the paper was to assess the cardiovascular consequences of CTX in CRC enrolled to the ONCOECHO multicentre study (2012-2014). To identify potential cardiotoxicity, we focused on myocardial function, heart rhythm and conduction disorders, and adverse cardiovascular events. Twenty-five CRC patients (12 women, mean age 61.3 [35-76] years), all receiving six-month adjuvant CTX were included. Thirteen patients received 5-fluorouracil (5FU)-based CTX, and 12 patients received a capecitabine-based scheme. Subjects were assessed at baseline and followed-up three, six, and 12 months after the onset of treatment. In this analysis we focused on conduction abnormalities, systolic and diastolic function of the left ventricle (LV), and cardiovascular events. In 12-month follow-up a decrease of selected tissue Doppler parameters (e.g. S'IVS, S'lat, and E'sept) was observed, and it was significant. LV structural parameters and ejection fraction (EF) remained unaffected. Changes in myocardial performance were not influenced by CTX regimen or treatment with beta-blockers or angiotensin-converting enzyme inhibitors. CTX did not affect LV structural parameters, EF, or conduction system, nor was it associated with cardiovascular events during the 12-month follow-up. CTX in CRC patients does not affect LV structural parameters and EF. It may, however, trigger subtle changes in myocardial performance detectable by tissue Doppler echocardiography after 12 months. Moreover, it causes a transient increase of QT, which resolves after CTX cessation.

Right Ventricle Segmental Strain Trends in Patients undergoing Tetralogy of Fallot Repair: An Observational Study

ABSTRACT Introduction Incidence of right ventricular (RV) dysfunction in early postoperative period after Tetralogy of Fallot (TOF) repair ranges from 28 to 63%. Echocardiography is the first-line tool for the assessment of RV function in early postoperative period. As speckle tracking echocardiography (STE) has emerged as a new promising tool for assessing myocardial performance and is independent of geometric assumptions and angle dependence, it is more sensitive for detecting changes in myocardial performance than conventional echocardiographic parameters of RV function. The current study demonstrates echocardiographic parameters assessed by conventional two-dimensional (2D) echocardiography and STE in patients before and after TOF repair. Materials and methods Fifty-nine consecutive patients planned for complete intracardiac repair for TOF were enrolled in this prospective cohort study. The 2D echocardiography and STE were performed a day prior to TOF repair, in the early postoperative period between days 3 and 7 and after discharge at 3 months. Results The median age of patients was 6 years, with 57.6% males (34/59). Baseline hemoglobin and room air oxygen saturation were 17.7 ± 3.7 gm% and 79.4% ± 8% respectively. Two patients did not survive the procedure (3.4%). Right ventricular longitudinal peak systolic strain (RV LPSS) in early postoperative period was significantly decreased in all segments of both septal and lateral wall. However, RV LPSS assessed at midterm follow-up at 3 months postoperatively significantly improved in all segments of RV compared with assessment done in the early postoperative period, and was significantly better than preoperative values in all three segments of the septal wall. Conclusion Our study shows that the use of 2D strain or speckle tracking is a feasible and easy-to-implement technique for the evaluation of RV function after TOF repair. How to cite this article Negi SL, Puri K, Mandal B, Rana SS, Barwad P. Right Ventricle Segmental Strain Trends in Patients undergoing Tetralogy of Fallot Repair: An Observational Study. J Perioper Echocardiogr 2016;4(2):45-50.

Serial changes in myocardial function in preterm infants over a four week period: the effect of gestational age at birth

Myocardial performance is impaired in the first days of life in preterm infants but improves by day 5. Tissue Doppler imaging (TDI) is a novel and reliable means of assessing myocardial performance. To investigate myocardial performance using TDI and shortening fraction (SF) in preterm infants of different gestational age groups and serial changes in these parameters in first four weeks of life. Study design Infants less than 36 weeks of gestation were divided into group 1 (24-27 weeks, n=8), group 2 (28-31 weeks, n=12) and group 3 (32-35 weeks, n=13). Infants with severe congenital malformations, a hypoxic insult at birth, and those on inotropic support were excluded. Echocardiograms were performed at 36-48 hours, 2 weeks and 4 weeks of life. Left ventricular (LV) SF, systolic (S'), early diastolic (E') and late diastolic (A') TDI velocities were assessed. We analyzed the data using a repeated-measures ANOVA. Thirty three infants underwent serial TDI and SF measurements. There was an increase in LV S' (p=.02) and E' (.01) velocities in group 2 , and in group 3 (p=.03 for S' and p=.04 for E'), but no significant increase in group 1 (p=.48 for S' and .32 for E'). At each study point, there was significant difference in myocardial performance between group 1 and 3 for each of the parameters (p<.05). There was no significant increase in SF over time in any of the groups. We describe a serial increase in myocardial performance in infants of 28 weeks gestation and above. While there was no change in myocardial performance among the most extremely preterm infants, this may have been the result of small sample size of the group.

324: Utility of Tei index in the selective reduced uterine perfusion pressure model of hypertension induction

Myocardial performance index or Tei index has been studied in several cardiac disorders and found to predict morbidity and mortality. Little is known about the changes of myocardial performance in preeclampsia as well as the utility of Tei index in predicting complications. The objective of this study was to assess the utility of the Tei index in detecting changes in myocardial performance in preeclampsia using the selective reduction of uterine perfusion pressure (SRUPP) model of hypertension induction in the pregnant rat.

Serial change in myocardial tissue Doppler imaging from fetus to neonate

Our goal was to evaluate the serial change in myocardial performance from fetus to neonate using tissue Doppler imaging (TDI). There were 37 term infants in the present study. The TDI sensor was placed at the level of the lateral mitral annulus (M-TDI), inter-ventricular septum (IVS-TDI) and the lateral tricuspid annulus (T-TDI). We measured TDI parameters from fetus to neonate. On univariate analysis, E' (cm/s), A' (cm/s), and S' (cm/s) of three ventricular walls of TDI parameters excluding E' IVS-TDI significantly decreased during the transition from fetal to neonatal circulation. E'/A' ratio, E/E' ratio and myocardial performance index (MPI) of three ventricular walls of TDI parameters excluding T-TDI MPI significantly increased during the transition from fetal to neonatal circulation. When multiple linear regression analysis with a step-wise procedure during the transition from fetus to neonate for TDI parameters was applied to variables, significant differences were noted for predicting decreases in M-TDI S' (6.55 to 3.97, p < 0.001) and IVS-TDI A', (6.69 to 4.69, p < 0.001), and increases in IVS-TDI E'/A' ratio (0.77 to 1.02, p < 0.001) and IVS-TDI E/E' ratio (8.25 to 13.65, p < 0.001). In conclusion, we found that the myocardial performances of both ventricles decreased during the transition from fetus to neonate using TDI parameters. In particular, left ventricular systolic performance was affected more than when fetal circulation changed to neonate circulation. Our findings suggest that serial change in TDI can give new information to estimate myocardial performance of the neonate.

Acute Changes in Myocardial Systolic Function in Preterm Infants Undergoing Patent Ductus Arteriosus Ligation: A Tissue Doppler and Myocardial Deformation Study

Ligation of a patent ductus arteriosus (PDA) in preterm infants causes profound hemodynamic changes that can result in low cardiac output syndrome and hypotension. The effect of PDA ligation on left ventricular myocardial function has not been studied using tissue Doppler and myocardial deformation imaging, mainly because of the limited validation of these methods in preterm infants. The primary objective of the present study was to determine the feasibility and reliability (intraobserver and interobserver variability) of tissue Doppler and myocardial deformation imaging for evaluating myocardial function in preterm infants undergoing surgical PDA ligation. Additionally, we sought to study the immediate effect of surgical ligation on the left ventricular tissue Doppler and strain measurements in the first 24 hours after surgery. Echocardiography was performed in 19 preterm infants before, 1 hour after, and 18 hours after PDA ligation born at 24-29 weeks of gestation. The tissue Doppler velocities of the lateral tricuspid and lateral and septal mitral valve annuli were obtained. The global and regional longitudinal peak systolic strain values were determined using two-dimensional speckle tracking echocardiography. The results of the three measurement points were compared using repeated measures analysis of variance. The intra- and interobserver variability was assessed using the intraclass correlation coefficient and Bland-Altman analysis. The median gestational age was 25.0 weeks (interquartile range 24.9-25.9) and the birth weight was 750 g (interquartile range 600-810). For the global longitudinal strain, the intraobserver intraclass correlation coefficient was 0.92 (95% CI, 0.78-0.97, P < .001), and the interobserver intraclass correlation coefficient was 0.93 (95% CI, 0.66-0.98, P < .001). Bland-Altman analysis showed no significant bias between the two observers, with good agreement. The systolic and diastolic tissue Doppler velocities of the mitral valve decreased significantly immediately after ligation and remained significantly lower than the preoperative levels at 18 hours. Also, the global longitudinal strain values significantly decreased 1 hour after the procedure (global longitudinal strain before -19.7% ± -3.8% vs -11.5% ± -3.5%; P= .001) but had significantly improved 18hours after the procedure (-15.1% ± -2.9%, P= .01). The present study has shown the feasibility and reliability of using tissue Doppler and strain imaging in premature infants with a hemodynamically significant PDA. Significant changes in myocardial function were observed immediately after PDA ligation, suggesting important changes in myocardial performance immediately after ductal ligation.

Doppler velocimetry of fetal pericardial fluid

To investigate the flow of normal fetal pericardial fluid (PF) with increasing gestational age using Doppler velocimetry. Ninety-five fetuses between 18 and 37 weeks of gestation with PF within the normal range were studied. PF was measured in 4-chamber view using M-mode or real-time ultrasound. Color Doppler was used to display and guide the pulse wave assessment of PF flow. PF waveforms as well as systolic and diastolic velocities were recorded and correlated with gestational age. PF was detected in all of the fetuses. The mean thickness of the PF rim was 0.95+/-0.45 mm. PF flowed toward the cardiac apex during systole and toward the atrium during diastole. PF waveforms showed bidirectional flow in all fetuses. The flow velocity PF was positively correlated with gestational age in both systole and diastole. Flow velocity of fetal PF increases linearly in both systole and diastole with gestational age. This might indirectly indicate a maturational change in myocardial performance as myocardial velocity is increased.

Mechanisms Underpinning Exercise-Induced Changes in Left Ventricular Function

Despite a growing body of evidence suggesting that prolonged strenuous exercise (PSE) is associated with a transient reduction in right (RV) and left ventricular (LV) performance, the exact mechanism(s) responsible for this phenomenon is not fully understood. As such, the primary objective of this article was to critically review the available literature (both animal and human) to provide insight into the potential mechanism(s) responsible for the development of "exercise-induced cardiac fatigue." We pay particular attention to the major mechanisms that have been linked to transient changes in systolic function after PSE including altered loading conditions, myocardial ischemia/damage, altered beta-receptor responsiveness, and altered cardiac autonomic modulation. We also examine the potential mechanisms that may contribute to transient changes in diastolic function often observed after PSE including changes in LV pressure gradients and alterations in intrinsic myocardial relaxation. Although further mechanistic investigations are clearly warranted, several key mechanisms have received support for at least a partial contribution to the transient changes in myocardial performance often observed after PSE.

Influence of oxygen tension on myocardial performance. Evaluation by tissue Doppler imaging

BackgroundLow O2 tension dilates coronary arteries and high O2 tension is a coronary vasoconstrictor but reports on O2-dependent effects on ventricular performance diverge. Yet oxygen supplementation remains first line treatment in cardiovascular disease. We hypothesized that hypoxia improves and hyperoxia worsens myocardial performance.MethodsSeven male volunteers (mean age 38 ± 3 years) were examined with echocardiography at respiratory equilibrium during: 1) normoxia (≈21% O2, 79% N2), 2) while inhaling a hypoxic gas mixture (≈11% O2, 89% N2), and 3) while inhaling 100% O2. Tissue Doppler recordings were acquired in the apical 4-chamber, 2-chamber, and long-axis views. Strain rate and tissue tracking displacement analyses were carried out in each segment of the 16-segment left ventricular model and in the basal, middle and apical portions of the right ventricle.ResultsHeart rate increased with hypoxia (68 ± 4 bpm at normoxia vs. 79 ± 5 bpm, P < 0.001) and decreased with hyperoxia (59 ± 5 bpm, P < 0.001 vs. normoxia). Hypoxia increased strain rate in four left ventricular segments and global systolic contraction amplitude was increased (normoxia: 9.76 ± 0.41 vs hypoxia: 10.87 ± 0.42, P < 0.001). Tissue tracking displacement was reduced in the right ventricular segments and tricuspid regurgitation increased with hypoxia (7.5 ± 1.9 mmHg vs. 33.5 ± 1.8 mmHg, P < 0.001). The TEI index and E/E' did not change with hypoxia. Hyperoxia reduced strain rate in 10 left ventricular segments, global systolic contraction amplitude was decreased (8.83 ± 0.38, P < 0.001 vs. normoxia) while right ventricular function was unchanged. The spectral and tissue Doppler TEI indexes were significantly increased but E/E' did not change with hyperoxia.ConclusionHypoxia improves and hyperoxia worsens systolic myocardial performance in healthy male volunteers. Tissue Doppler measures of diastolic function are unaffected by hypoxia/hyperoxia which support that the changes in myocardial performance are secondary to changes in vascular tone. It remains to be settled whether oxygen therapy to patients with heart disease is a consistent rational treatment.

Effects of different inotropic interventions on myocardial function in the developing rabbit heart

The development of the mammalian heart is characterized by substantial changes in myocardial performance. We studied the ontogeny of myocardial function with and without various inotropic interventions in the developing isolated, antegrade-perfused rabbit heart (2d, 8d, 14d, 28d, n = 96). Myocardial function was related to the protein expression of the sarcolemmal Na(+)-Ca2+ exchanger and to the sarcoplasmic Ca(2+)-ATPase. In neonatal hearts an age-dependent increase in maximal developed pressure velocity (dP/dtmax) by 45% and peak negative pressure velocity (dP/ dtmin) by 75% within days 2 to 8 were observed. In response to inotropic intervention with isoproterenol, ouabain, calcium and the Na(+)-channel modulator BDF 9148, dP/dtmax and dP/dtmin increased in a concentration dependent manner. Significant differences between neonatal, juvenile and adult hearts could be demonstrated in a repeated measurement ANOVA model on the concentration-response curves for BDF 9148 (dP/dtmax and dP/dtmin), ouabain (dP/dtmin) and calcium (dP/dtmin), but not for isoproterenol. At the maximum isoproterenol concentration of 1 micromol/l, the increase in dP/dtmax and dP/dtmin was significantly higher in adult compared to neonatal hearts (t-test, p < 0.01). The significant decline of the Na(+)-Ca2+ exchanger protein expression from neonatal (1822 +/- 171) to adult hearts (411 +/- 96 S.E.M. [units per 20 microg protein], p < 0.01) was related to an increase in myocardial function (dP/dtmax r = 0.63, p < 0.01, dP/dtmin r = 0.62, p < 0.01). Contractility, relaxation and the observed positive inotropic effects were in general significantly lower in neonatal compared to adult hearts. In the individual heart an increase in contractility and relaxation was related to a decrease in Na(+)-Ca2+ exchanger expression.

Myocardial performance and baroreceptor reflexes in preterm neonates: an echocardiographic evaluation using the tilt-table test.

The hemodynamic consequence of head-up position in preterm infants is not known, so we used the tilt-table test to assess changes in myocardial performance and baroreceptor reflexes. Twenty-five preterm infants with gestational age (GA) (mean +/- SD) 31 +/- 2.9 weeks (range 25-35.5 weeks), birth weight of 1612 +/- 642 g (range 520-3260 g) were studied in supine, 30 degrees, and 60 degrees head-up positions. GA had a significant effect on heart rate (HR) (p = 0.007), systolic blood pressure (SBP) (p = 0.03), left ventricular (LV) cavity dimensions (p = 0.001), cardiac output (CO) (p = 0.001), LV ejection time (LVETc) (p = 0.05), and end systolic wall stress (ESWS) (p = 0.003). An inverse relationship was seen between velocity of circumferential fiber shortening (VcFs) and ESWS (slope b = -0.019 +/- 0.008, p = 0.003). Results of tilt tests showed that at supine, 30 degrees, and 60 degrees, respectively, HR was 162 +/- 10.5, 162 +/- 9, and 164 +/-12 (p = NS); SBP (mmHg) was 73 +/- 11, 72.5 +/- 9.5, and 78 +/- 10 (p = NS); CO (L/kg/min) was 0.4 +/- 0.16, 0.4 +/- 0.15, and 0.43 +/- 0.16 (p = NS); ESWS (g/cm2) was 38.7 +/- 8.3, 40.9 +/- 9.9, and 43.4 +/- 10.7 (p = NS); and VcFs (circ/sec) was 1.35 +/- 0.3, 1.28 +/- 0.4, and 1.26 +/- 0.2 (p = NS). LV filling pattern as seen by early/late atrial Doppler flow velocity ratio did not change with tilt (p = NS). Myocardial performance improved with increasing GA. No significant differences in myocardial performance were found between baseline and head-up tilt positions.

Cerebral blood flow velocity wave form as an indicator of neonatal left ventricular heart function

To investigate the relationship between cerebral blood flow velocity wave form (CBFV-WF) parameters and myocardial contractility indices in healthy and sick preterm and term newborns. Total group of 82 babies was divided into four subgroups: prematures with gestational age <34 weeks with (n=20) and without (n=14) respiratory distress syndrome (RDS) and infants with gestational age of >33 weeks with (n=18) and without (n=30) asphyxia. On day 1, 2, 3, 6 and 14, the acceleration time, Q(ECG)-peak(flow) time and preejection period of CBFV-WF (internal carotid artery) were measured through the anterior fontanel by Doppler ultrasonography. Simultaneously cardiac output, fractional shortening, systolic time intervals and their ratio were determined echocardiographically. RDS-babies had higher cardiac output and better myocardial performance then non-RDS-babies. Asphyxiated babies had lower cardiac output as compared to healthy babies, improving over time. Correlations were found between CBFV-WF parameters and several myocardial function indicators, but preejection period of cerebral blood flow velocity correlated closest with the same period measured echocardiographically (r=0.67, P<0.0001). Multiple linear regression revealed no influence of gestational age or clinical condition on this relationship. Assessment of agreement indicated that only substantial changes in myocardial performance could be monitored using preejection period of CBFV. Although a relationship was detected between the preejection period of CBFV and left ventricular systolic time interval (used as indicator of changes in left ventricular function), only rather large changes in left ventricular performance can be reliably detected using the preejection period of CBFV.

Cardiac function at rest in hypothyroidism evaluated by equilibrium radionuclide angiography.

Previous studies have suggested that hypothyroidism affects both systolic and diastolic cardiac function. We have applied equilibrium radionuclide angiography to the study of heart function at rest in hypothyroidism. A prospective study, evaluating cardiac function at rest in primary hypothyroidism. Cardiac function was studied by means of equilibrium radionuclide angiography. Screening echo-Doppler examinations were performed on each patient. Twenty-six consecutive untreated hypothyroid patients without clinical or echocardiographic cardiac disease and 20 healthy matched controls. Between patients and controls, the time to peak emptying rate (161 +/- 6 msec vs. 144 +/- 6 msec, P < 0.05) and the time to peak filling rate (188 +/- 6 msec vs. 170 +/- 5 msec, P < 0.05), were the only discriminatory parameters. In hypothyroid patients, a trend towards a decrease in diastolic cardiac function, expressed as peak filling rate, was observed: 2.6 +/- 0.1 End Diastolic Volume (EDV)/s vs. 3.0 +/- 0.1 EDV/s, P = 0.06. Within the hypothyroid patient group, the time to peak emptying rate was more prolonged in patients with lower free thyroxine levels (R = -0.60, F = 13.5, P < 0.001). Peak filling rate was decreased in patients with lower free thyroxine levels (R = 0.51, F = 8.4, P < 0.01) whereas the time to peak filling rate was more prolonged (R = -0.62, F = 15, P < 0.001). In a large group of consecutive patients presenting with primary hypothyroidism, even in the absence of clinical cardiac disease and echocardiographic abnormalities, clear changes in myocardial performance at rest were observed. The most obvious effect of thyroid hormone deficiency on the heart was a lengthening of both systolic and early diastolic time characteristics. Diastolic rather than systolic cardiac function was influenced by hypothyroidism.

740-5 A New Intracavitary Cathether for Monitoring Contractility Through Endocardially Recorded First Heart Sound: Initial Clinical Validation

Theoretical and experimental evidences have shown how changes in myocardial performance are mirrored in changes of first heart sound acceleration amplitude, which is generally 10 to 100 times more powerful with endecavitary than with chest wall recordings. Aim of the study was to evaluate the clinical feasibility and tolerability of intracavitary sampling of first heart sound via an implantable tip mounted accelerometer in man. We developed an unidirectional acceleration sensor (Sorin Biomedica) located inside the stimulating tip of a standard unipolar pacing lead: it has a frequency response up to 1 KHz and a sensitivity of 5 mV/G (G = 9.8 m/sec 2 ). The lead was connected to an external signal amplifier with a frequency range of 0.05–1,000 Hz and to a peak to peak detector synchronised with the endocardial R-wave scanning the isovolumetric contraction phase. Following standard electrophysiologic studies, sensor equipped leads were temporarily inserted in the right ventricle of 15 patients (61 ± 7 years), with normal regional and global ventricular function, to record peak endocardial acceleration (PEA) of first heart sound frequencies at rest, during AAI pacing, VVI pacing and during dobutamine infusion (up to 20 mcg/kg/min). PEA at baseline was 1.2 ± 0.6 G (heart rate = 68 ± 13 b.p.m.1 and increased to 1.5 ± 0.9 (p = ns vs baselinel during AAI pacing (heart rate = 140 b.p.m.) and to 1.4 ± 0.7 (p = ns vs baseline) during VVI pacing (heart rate = 140 b.p.m.). Dobutamine infusion increased PEA to 5.4 ± 2.1 (p &lt; 0.001 vs baseline). with a heart rate = 120 ± 11 b.p.m. In conclusion, high quality first heart sound recording can be consistently and safely obtained with an implantable device. Pharmacologic inotropic stimulation, but not isolated chronotropic stimulation, increase the strength of the signal, in keeping with the experimental studies suggesting that PEA is an index of myocardial contractility. The clinical applicability of the method via right heart catheterization and implantable device offers potential for new diagnostic applications.

Independent role of arterial O2 tension in local control of coronary blood flow

The aim of this study of a blood-perfused isolated rabbit heart preparation was to differentiate the effects on coronary resistance of large changes in arterial O2 tension (arterial PO2 = 45-400 Torr) from the effects of variations in arterial O2 content or myocardial O2 delivery. Standard stored human blood was resuspended in Krebs-Henseleit buffer and was oxygenated to obtain normal PO2, high PO2, and low PO2. Hemoglobin concentrations were adjusted to obtain the same arterial O2 content (CaO2) for the three PO2s. In a first set of experiments, in which coronary blood flow (CBF) was free and adapted to a constant perfusion pressure, switching from control [138 +/- 17 (SE) Torr] to high PO2 blood (380 +/- 27 Torr) induced a significant decrease in CBF and myocardial O2 consumption (MVO2). Switching from control (125 +/- 3 Torr) to low PO2 blood (49 +/- 5 Torr) induced a significant increase in CBF and MVO2. In a second set of experiments, the switch from control (159 +/- 5 Torr) to high PO2 (389 +/- 32 Torr) was performed in a preparation in which CBF and consequently O2 delivery were constant. Under these conditions, the increase in perfusion pressure demonstrated that PO2 affected coronary resistance, even though the O2 delivery was constant. No significant change in myocardial performance was observed in any of these experimental procedures. These results show that arterial PO2 may affect coronary blood flow regulation independently of any mediation by the autonomic nervous system and of any associated changes in O2 content or O2 delivery.

Pattern of hemodynamic alterations during coronary artery operations

Twenty-four patients were studied to determine the relative importance of cardiac and peripheral factors in the hemodynamic changes associated with coronary artery operations. None had preoperative evidence of ventricular impairment. Anesthetic management was standardized for all. Sequential hemodynamic measurements revealed the following: (1) Five minutes following induction of anesthesia, all hemodynamic indices were stable except for an increase in heart rate (p less than 0.001). Sternotomy and pericardiectomy were followed by a drop in cardiac index (p less than 0.01) and systolic blood pressure (p less than 0.01). (2) Late during bypass, there was a significant, parallel reduction in both hematocrit and systemic vascular resistance (SVR) (p less than 0.001 and 0.01, respectively). (3) Five minutes after termination of bypass, cardiac output was markedly elevated (p less than 0.001) in association with a decrease in SVR (p less than 0.001), marked hemodilution (p less than 0.001), and tachycardia (p less than 0.001). (4) Following sternal closure, and despite the fact that the hematocrit was still reduced (p less than 0.001), there developed a trend of increased mean arterial pressure (MAP) and SVR with a reduction in cardiac index. These changes were further accentuated 1 hour postoperatively. The SVR was 33% higher than in the previous stage (p less than 0.01), whereas the high cardiac index recorded with initiation of bypass declined significantly to preoperative values. Throughout the studies, there was a strong correlation between alterations in hematocrit and changes in cardiac index and SVR. Blood pressure variations showed no correlation with changes in cardiac output but were significantly related to alterations of peripheral resistance. Sequential determinations of plasma renin activity and catecholamine levels showed no significant alterations in either. The alterations reported describe not only group averages but also the behavior of every patient investigated. The results suggest that in patients with normal or only mild left ventricular impairment, the major factor influencing arterial pressure variations during coronary artery operations and in the postoperative period was the change in peripheral resistance rather than alterations in cardiac output. In the treatment of hypotension under these conditions, one should take into account variations in peripheral vascular resistance and not depend solely on assumed changes in myocardial performance.

Biochemical and physiologic effects of thyroid hormone on cardiac performance

Abstract Recognition of the existence of ventricular myosin isozymes and their regulation by thyroid hormone may provide a biochemical basis for some of the effects of the hormone on myocardial performance. The isozymes, which are referred to as V 3 , in order of decreasing electrophoretic mobility and ATPase activity, contain the same light chain components, but differ in their heavy chain composition. V 1 contains two A heavy chains, V 3 two B heavy chains, and V 2 one heavy chain of each type. Rabbit and several other mammalian species, including man, have a predominance of the low activity V 3 form. The relative proportions of these myosin forms seems consistent with a random association of the heavy chain types. Thyroid hormone administration leads to a predominance of the high activity V 1 form of the enzyme, indicating that A chain synthesis has been stimulated and B chain synthesis suppressed. By contrast, the V 1 form normally is predominant in rat ventricle; thyroid ablation procedures lead to expression of the V 3 form, indicating stimulation of B chain synthesis and suppression of A chain synthesis. Since the ATPase activity of myosin seems closely related to the intrinsic speed of cardiac contraction, a change in myosin isozyme composition from V 3 to the V 1 may explain the increase in velocity of shortening observed in papillary muscles from thyrotoxic cat and rabbit hearts. Similarly, the switch from V 1 to V 3 may account for the decrease in performance of hypothyroid rat cardiac muscle. However, in man and other species which normally have a predominance of the V 3 form, the reported changes in myocardial performance in hypothyroidism may be related to other factors, including alterations in electro-mechanical coupling, myxedematous infiltration and coronary atherosclerosis. Assessments of LV performance in thyrotoxic subjects and in conscious animal models have indicated that LV wall velocity is not usually greater than normal because of the increase in afterload. Although LV systolic and diastolic dimensions are often increased, ventricular filling pressures remain normal, and there is no evidence of sarcomere stretching or disruption. Acute B-adrenergic blockade has very little influence on any of these alterations in LV performance. Furthermore, animal experiments and computer simulation of the thyrotoxic circulatory system indicate that there are important changes in the peripheral vascular compartments as well as in the heart. These alterations, which include a decrease in peripheral arterial resistance and an increase in P ms , should be regarded as essential features of the high-output state associated with thyrotoxicosis. A change from the V 1 to the V 3 form also has been shown to occur in the rat ventricle during development, aging, chemically-induced diabetes, and in hemodynamic overload. In some cases, these changes seem to be associated with alterations in plasma thyroid hormone concentration. Also, in diabetes and pressure overload, the changes in myosin isozyme composition can be reversed by thyroxine treatment. Taken together, the experimental data suggest that thyroid hormone may play at least a permissive role in regulating ventricular myosin isozyme expression in many nonthyroidal cardiac conditions. The potential to alter myosin isozyme composition constitutes an important area for future research.

Radionuclide assessment of sequential changes in left and right ventricular function following first acute transmural myocardial infarction

The purpose of this study was to define the sequential changes in left and right ventricular ejection fraction (LVEF, RVEF) and regional LV wall motion following first transmural acute myocardial infarction (AMI). Fifty-four patients with either anterior (n = 28) or inferior (n = 26) infarction underwent radionuclide ventriculography (RNV) within 48 hours of onset of chest pain (study 1), between days 3 and 6 (study 2), and again between days 7 and 25 (study 3). Twenty-six of the patients with anterior MI (93%) had initial LVEF less than 0.54, compared with 13 of 26 patients (50%) with inferior MI (p less than 0.01). Eleven of 26 patients (42.3%) with inferior MI had initial RVEF less than 0.39, compared with 8 of 27 patients (29.6%) with anterior MI (p less than 0.01). There were no overall significant serial changes in mean LVEF or mean RVEF in patients with either anterior or inferior MI. From study 1 to study 2, LVEF did not change in 24 patients (44%), improved in 13 (24%), and worsened in 17 (31%). From study 1 to study 3, LVEF remained unchanged in 15 patients (35%), improved in 17 (39%), and worsened in 11 (26%). From study 1 to study 2, RVEF did not change in 25 of 51 patients (49%), improved in 17 (31%), and worsened in 9 (17%). From study 1 to study 3, RVEF remained unchanged in 14 (38%), improved in 18 (48%), and worsened in five (14%). Changes in EF tended to occur early in the hospital course, with little subsequent changes. Serial changes in EF could not be predicted by clinical or demographic variables or by location of infarction. Significant changes in LVEF typically occurred without concurrent change in regional LV wall motion, suggesting alteration in ventricular loading rather than change in intrinsic myocardial performance. Initial depression of LVEF correlated with in-hospital mortality as well as with development of congestive heart failure and conduction defects. However, sequential changes in LVEF did not correlate with short-term prognosis. We conclude that sequential changes in LVEF and RVEF occur frequently following AMI, appear to reflect ventricular loading conditions rather than intrinsic change in myocardial performance, and do not correlate well with short-term prognosis.

Use of radionuclide ventriculography for assessment of changes in myocardial performance induced by disopyramide phosphate

Disopyramide phosphate may precipitate heart failure in susceptible patients with cardiomegaly. To identify those at risk, gated radionuclide ventriculography (RVG) was performed in two groups. Eleven patients without evidence of structural heart disease constituted group 1, and 12 with impaired ventricular function made up group 2. RVG was carried out before and 2 hours after administration of a single 300-mg dose of disopyramide orally. After disopyramide mean left ventricular ejection fraction (EF) decreased in the 12 patients in group 2 (35% to 26%) (p less than 0.01); depression of function was most pronounced in regions with the poorest baseline value. Of the 11 patients in group 1 (mean EF 60%), EF was reduced after disopyramide in only one. Serum levels of drugs were comparable in patients in both groups (3.1 vs. 3.7 micrograms/ml). We conclude that (1) patients with left ventricular dysfunction are particularly susceptible to the depressant effects of disopyramide; (2) RVG is a sensitive technique for detecting disopyramide-induced changes in ventricular performance; and (3) RVG before and shortly after a dose of disopyramide orally may help to identify those patients at high risk.